The document summarizes a talk about analyzing the rest-frame UV spectrum of a galaxy called the Cosmic Horseshoe at z~2 using spectroscopy. Key points include analyzing the stellar spectrum, interstellar spectrum, and Lyman alpha emission feature to determine properties like the stellar population, gas outflows, and metallicity. Comparisons are made to another lensed galaxy, MS1512-cB58, showing similarities in winds and metallicity. Broad conclusions relate to metallicity indicators, the potential for Lyman continuum photon leakage, and cautions around interpreting Lyman alpha profiles.

1. The Cosmic Horseshoe:
The Rest-frame UV
Spectrum of a z~2 LBG
Anna Quider
Institute of Astronomy
University of Cambridge
Max Pettini (IoA), Alice Shapley (UCLA), Charles Steidel (Caltech)

2. Today’s Talk
‣ Overview of Lyman Break Galaxies (LBGs) and
rest-frame UV spectroscopy
‣ Results from the Cosmic Horseshoe
- Stellar spectrum
- Interstellar spectrum
- Lyman alpha emission feature
‣ Broader conclusions from the Cosmic Horseshoe
‣ Summary
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

3. The Universe

4. The Universe
Galaxies from about 2 to 3 billion years
after the Big Bang

5. What is a LBG?
‣ High z starforming galaxy
identified by the Lyman
break photometric
selection technique
‣ Criteria for 2 ≤ z ≤ 2.5:
R ≤ 25.5
G - R ≥ -0.2
G - R ≤ 0.2 (Un - G) +0.4
(Un - G) ≥ (G - R) + 0.2
(Un - G) ≤ (G - R) + 1.0
(Steidel et al. 2004)
(Adelberger et al. 2004)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

6. garding how the UV LF evolves at high redshift. While some stud- evolve
ies have argued that the evolution primarily occurs at the bright (2006)
Cosmic Context
end (i.e., Dickinson et al. 2004; Shimasaku et al. 2005; Ouchi et al.
2004a; Bouwens et al. 2006, 2007; Yoshida et al. 2006), there
from z
of resu
have been other efforts which have argued that the evolution oc- very st
higher
the UV
ficient
2003,
z k 7,
numbe
dropou
2007)
Table 7
À20:5
(see al
Stanwa
bright
The
of UV
et al. (2
(Bouwens et al. 2008)
cluster
Fig. 9.—Estimated star formation rate density as a function of redshift (inte- that a s
Anna Quider down to 0.2 LÃ as in Fig. Horseshoe: UV of points give the SFR density
grated The Cosmic 8). The lower set Spectrum
z¼3 Institute of Astronomy al. (
et

7. garding how the UV LF evolves at high redshift. While some stud- evolve
ies have argued that the evolution primarily occurs at the bright (2006)
Cosmic Context
end (i.e., Dickinson et al. 2004; Shimasaku et al. 2005; Ouchi et al.
2004a; Bouwens et al. 2006, 2007; Yoshida et al. 2006), there
from z
of resu
have been other efforts which have argued that the evolution oc- very st
higher
the UV
ficient
2003,
z k 7,
numbe
dropou
2007)
Table 7
À20:5
(see al
Stanwa
bright
The
of UV
et al. (2
(Bouwens et al. 2008)
cluster
Fig. 9.—Estimated star formation rate density as a function of redshift (inte- that a s
Anna Quider down to 0.2 LÃ as in Fig. Horseshoe: UV of points give the SFR density
grated The Cosmic 8). The lower set Spectrum
z¼3 Institute of Astronomy al. (
et

8. Local Galaxies
Early Galaxies
(Bouwens et al. 2008)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

9. What’s visible in a galaxy?
ga
la
xy Gas
? Dust
Stars
Also: planets, comets, asteroids...but too small to see

10. Studying Galaxies Using
How can you study galaxies?
Spectroscopy
Using Spectroscopy!
Light is split into its component wavelengths so that we
galax
can directly study the stars and gas in the galaxy
galaxy?
Text
Light from stars
y?
Hot, ionized gas
close to stars
Cold gas between
stars
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

11. Stars are Blackbodies
Very red (cool)
• Different wavelengths probe
different stellar populations
Very blue (hot)
• Rest-frame UV spectroscopy probes
the most massive, youngest stars
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

12. Aside:
Astronomy Naming Conventions
Any element heavier than Hydrogen or Helium
is called a “metal” (e.g. C, N, O, Fe, Ni, Si, etc.)
O I = neutral oxygen
O II = singly ionized oxygen
O III = doubly ionized oxygen
etc.
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

13. Rest-frame Optical Spectra
H II region
emission lines
are very visible
and therefore are
relatively easy to
study
(Erb et al. 2006a)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

14. Rest-frame Optical Spectra
Median Values for z~2 LBGs
SFR ~23 MO/yr
Z 0.4 to 1.0 ZO
E(B-V) 0.15
σ ~100 km/s
Age 570 Myr
M❋ 2 x 1010 MO
(Erb et al. 2006a,b,c)
(Erb et al. 2006a)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

15. Rest UV Spectral Features
Low Ion IS Abs
High Ion IS Abs
Stellar Abs
Nebular Em
Stellar Em
H I Em/Abs
(Shapley et al. 2003)
A mix of features from hot OB stars, low and high
ionization interstellar gas, and the H II regions
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

16. What about a detailed study of the
stars, interstellar gas, and H II regions
in an individual LBG?
The answer:
Strongly gravitationally lensed LBGs!
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

17. Gravitational Lensing
Gravity distorts and magnifies light from distant galaxies
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

18. MS1512-cB58
‣ Serendipitously found in cluster
MS1512+36 (z=0.37)
‣ zcB58 = 2.7276
‣ Magnified ~ 30x and L ~ L*
Nitrogen
(www.eso.org)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

19. MS1512-cB58
‣ Stellar population (metallicity, IMF)
‣ Interstellar abundances
Relative Flux
‣ Large-scale outflows
‣ Lyman-α feature morphology Relative Velocity (km s-1)
Relative Flux
α-capture
Fe-peak Relative Velocity (km s-1)
Nitrogen
Figures from Pettini et al. 2002
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

20. Cosmic Horseshoe
‣ 10” Einstein Ring
‣ Discovered by Belokurov et al. (2007) in SDSS
‣ 24±2x magnification (Dye et al. 2008)
‣ L ≈ 2.4L*
‣ zCH = 2.38115
From rest-frame optical spectrum:
‣ SFR = 100 MO/yr
‣ Mvir ≈ 1.4 x 1010 MO
‣ Z ≈ 0.5-1.5 ZO
(Hainline et al. 2009)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

21. ESI Spectrum
‣Echellette Spectrograph and Imager (ESI) spectrum
- Keck II telescope
- 4000 - 10000 Å coverage
(1184 - 2959 Å restframe)
- 11.4 km s-1 pixel-1 resolution
- 36100s total exposure
- Spectra of two knots
(Quider et al. 2009; courtesy
of Dr. Lindsay King)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

22. 10 ly
A high z star-forming galaxy has many regions like this
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

23. Hot, young stars
Cavity caused by
To Earth
stellar wind
10 ly
A high z star-forming galaxy has many regions like this
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

24. Hot, young stars
Cavity caused by
To Earth
stellar wind
10 ly
Gas being ionized by
the young, hot stars
(a H II region)
A high z star-forming galaxy has many regions like this
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

25. Hot, young stars
Cavity caused by
To Earth
stellar wind
10 ly
Gas being ionized by
the young, hot stars
(a H II region)
Cold interstellar gas
(interstellar absorption)
A high z star-forming galaxy has many regions like this
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

26. Stellar Photosphere
“1425” “1978”
“1425” Index:
‣ Blend of:
- Si III 1417
- C III 1427
- Fe V 1430
‣ ZOBstars = 0.5ZO
“1978” Index:
‣ Only Fe III
(Quider et al. 2009)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

27. Stellar Wind
C IV Wind Feature
(Quider et al. 2009)
‣ Complex superposition ‣ Wind due to most
massive O stars
- P-Cygni broad - narrow interstellar
emission/absorption absorption ‣ Starburst99 models
- photospheric broad - narrow nebular - Continuous SF
absorption emission - 100Myr old
- Salpeter IMF
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

28. Stellar Wind
ZOstars = 0.6ZO
MS1512-cB58 and
Cosmic Horseshoe
have very similar
winds!
(Quider et al. 2009)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

29. Interstellar Gas Absorption
Normalized flux
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

30. Interstellar Gas Absorption
Normalized flux
Gas moving away Gas moving towards
from the stars the stars
Structure of the interstellar absorption lines is interpreted as
being due to large-scale outflows of gas away from the stars
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

31. Interstellar Gas Absorption
‣ -800 km/s to +250 km/s
‣ Same for low and high
ionization gas
‣ Evidence for only ~60%
coverage of stars by
outflowing gas
(Quider et al. 2009)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

32. Lyman α Emission Feature
‣ Lyman α is from H I gas
‣ Double-peaked emission
‣ Kinematic structure:
- Peak 1 at +115 km/s
- Peak 2 at +275 km/s
- Red wing to +700 km/s
(Quider et al. 2009)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

33. a
Structure matches
well with outflow
model from b
Verhamme et al.
(2006).
c
NHI ~ 7 x 1019 cm-2
λ
Anna Quider λ
The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

34. What broader conclusions
can we draw from studying
the Cosmic Horseshoe?
‣ Comparison between different metallicity indicators
‣ Possible candidate for Lyman continuum photon leakage
‣ A cautionary note on over-interpreting Lyα profiles
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

35. Table 5. M Metallicity Indicators
C
ETALLICITY OMPARISON
Method Element(s) Z/Z a Comments
R23 O 1.5 H II regionsb
N2 O 0.5 H II regionsb
O3N 2 O 0.5 H II regionsb
1425 C, Si, Fe 0.5 Photospheric, OB stars c
1978 Fe ... Photospheric, B starsc
C IV C, N, O, Fe ∼ 0.6 Stellar wind, O starsd
(Quider et al. 2009)
a Abundance relative to solar (on a linear scale), using the
Good agreement abundances by Asplund et al. (2005).
compilation of solar
among different metallicity indicators
b As reported by Hainline et al. (2009).
c
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

36. Lyman Continuum Photons
C II 1334 O I 1302 Si II 1304
‣ 10-15% of Lyman alpha photons escape
‣ 60% covering of stars by interstellar gas may provide a
route for the escape of Lyman continuum photons
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

37. Lyman α Morphology
Cosmic Horseshoe
top 50% of LBGs
Similarities Lyα emission
Z~0.5ZO
Salpeter IMF
ΔvISM ~1000 km/s Relative Velocity
Relative Flux
(km s-1)
(Quider et al. 2009)
SFR~50-100 MO/yr
MS1512-cB58
Mvir~1-1.5x1010 MO top 25% of LBGs
Lyα absorption
Relative Velocity (km s-1) (Pettini et al. 2002)
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

38. Summary
• LBGs are high z starforming galaxies whose spectra show a wide
variety of Lyα profiles, ISM trends with Lyα strength, young
stellar populations, and gas with outflow speeds v ~ 200 km s-1
• Highly lensed LBGs are key to understanding the detailed
chemical, kinematic, and structural properties of LBGs, as
evidenced by the work on MS1512-cB58 and the Cosmic
Horseshoe
• More galaxies need detailed study to determine the range of
properties of high redshift starforming galaxies: stay tuned for the
Cosmic Eye, Cosmic Clone, and 8 o’clock Arc!
Anna Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

39. Rest UV Spectral Features
‣ Stellar Component:
Best-fit Starburst99 model is 300Myr,
continuous star formation,
Z = 0.25 ZO
‣ Interstellar Component:
Absorption strength and Δvem-abs vary
with Lyα emission strength for low-
ionization transitions but are constant
for high-ionization transitions
‣ Physical Picture:
Patches of neutral gas are embedded in
a continuous shell of high-ionization
gas, all of which is outflowing.
(Shapley et al. 2003)
(Steidel et al. 2003)
A. Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy

40. Interstellar Gas Absorption
(Quider et al. 2009)
Column densities and ~0.5ZO imply N(H I) ≈ 6x1020 cm-2
A. Quider The Cosmic Horseshoe: UV Spectrum Institute of Astronomy